WO2008110445A1

WO2008110445A1 - Diffuser arrangement

Info

Publication number: WO2008110445A1
Application number: PCT/EP2008/052222
Authority: WO
Inventors: Sascha Becker; Marc Bröker; Ralf Hoffacker; Mario Koebe; Stefan MÄHLMANN; Ulrich Stanka
Original assignee: Siemens Aktiengesellschaft
Priority date: 2007-03-13
Filing date: 2008-02-25
Publication date: 2008-09-18
Also published as: EP1970539A1; RU2009137901A; EP2140112A1; CN101680305A; US20100226767A1

Abstract

The invention relates to a diffuser arrangement (1) through which a fluid can flow, having an outer diffuser (2) comprising an inner surface, and a flow acceleration device (9), which is configured such that at least part of the boundary layer flow forming on the inner surface of the outer diffuser (8) can be accelerated in the main flow direction, so that a flow separation is prevented on the inner surface of the outer diffuser (8). Further, an evaporation chamber of a steam turbine, or an evaporation chamber of a gas turbine comprises the diffuser arrangement.

Description

description

diffuser assembly

The invention relates to a diffuser arrangement and more particularly to an exhaust steam room of a steam turbine or an exhaust gas space of a gas turbine with the diffuser arrangement.

A diffuser is a fluid-permeable channel which delays the fluid in a transfer-free flow through cross-sectional widening and according to Bernoulli's theorem reduces the kinetic pressure of the fluid in favor of the static pressure.

The quality of the diffuser is described by the pressure recovery coefficient associated with

Cp = (Paus ^~~ Pein) / (Ptotal, a ^~~ Pein)

and the total or total pressure P _tota i, _e m, the static pressure P _e in at the diffuser inlet and the static pressure p _out at the diffuser outlet.

For example, diffusers are used in pipelines for pressure recovery or for continuous bridging of cross-sectional extensions (transitional diffuser). In pipelines with a circular cross section, the diffusers are formed axially symmetrical. FIG. 4 shows a longitudinal section of an axially symmetrical diffuser 101 and schematically illustrates the flow typically occurring therein. The diffuser 101 has an inlet cross section 102 and an outlet cross section 103, whose area ratio is greater than one. Upstream of the diffuser 101, a cylindrical inflow pipe is arranged, through which an inflow 108 flows, and downstream of the diffuser 101 a cylindrical outflow pipe is arranged, through which an outflow 109 flows. Due to the adhesion of the fluid to the diffuser wall, a boundary layer is formed in the near-wall flow. In the lower half of the diffuser 101 shown in FIG. 4, five characteristic velocity profiles 110 to 114 are shown along the main flow direction, where the first two velocity profiles 110, 111 are the near-wall flow in the inflow pipe and the upstream three velocity profiles 112 to 114 are close to the wall Flow in the diffuser 101 show.

Since the flow in the diffuser 101 is retarded, the flow velocity of the main flow decreases in the flow direction, whereby the static pressure of the flow in the flow direction increases correspondingly, while satisfying the first law of thermodynamics. According to Prandtl 's boundary layer theory, the static pressure in the boundary layer is constant across the flow direction.

Due to the retarding effect of the diffuser 101 and the adhesive condition on the diffuser wall, the flow velocity of the near-wall flow decreases. After overcoming a certain flow path, the gradient of the flow velocity across and against the diffuser wall is zero. This location is a separation point 105 of the flow shown in the boundary layer profile 113.

At the separation point 105, the flow moves away from the diffuser wall toward the center of the diffuser 101, forming a return flow downstream of the separation point 105 near the wall forming a detachment bladder 106. The detachment bladder 106 causes a constriction of the effective cross-section of the diffuser 101, so that the main flow in the region of the detachment bladder 106 is accelerated. As a result, the kinetic energy increases in the main flow and the flow settles in the outlet pipe at a restart point 107 again. The degree of opening of the diffuser 101 shown in FIG. 4 decisively determines the shape and size of the peel-off bladder 106 and the location of the detachment point 105 and the optionally occurring reapplication point 107. The higher the degree of opening of the diffuser 101, the further upstream the detachment point 105 is.

Due to the narrowing of the effective cross section of the diffuser 101, the peel bladder 106 reduces the pressure recovery effect of the diffuser 101 compared to a diffuser in which the flow is fully applied.

In order to produce a laminar boundary layer flow in a diffuser, a paddle wheel seated on a hub is known from the published patent application DE 1 628 337, of which one of a

Diffuser sheet coated leaves are connected blade-tip side by a ring. On the ring, a ring of vanes is arranged such that it widens the stream of air flowing from the blade wheel while maintaining the edge flow guided by the diffuser plate. In addition to the guide vanes this is achieved in particular by the fact that the ring has a corresponding cross-sectional shape, which also favors the course of the entrained stream threads and blows them out at a higher speed.

Furthermore, in order to avoid flow separations in a diffuser from JP 08 260905, a pipe arranged parallel to the diffuser wall is known, which extends along the flow direction. Due to the diverging cross section of the diffuser and the parallel, correspondingly diverging tube, the flow cross-section of the annular channel formed between the diffuser wall and the tube increases, so that the medium flowing in the annular channel is delayed.

A steam turbine or a gas turbine is driven at partial, basic and overload. When designing and designing the steam or gas turbine, its individual components can be For example, be optimized in terms of efficiency or aerodynamic or thermodynamic efficiency optimized only in a single operating point geometrically. As a result, in other operating points that are not identical to the design operating point, the components can not operate optimally.

This situation also applies to an exhaust steam room of the steam turbine or an exhaust space of the gas turbine. The exhaust steam space or the exhaust gas space is conventionally designed as an axial diffuser.

As a rule, the axial diffuser is optimally designed geometrically with regard to the base load so that the axial diffuser can not be optimally operated with partial and overload.

At the entrance of the axial diffuser there is a lower static pressure than at the outlet with optimal design. By lowering the pressure at the diffuser inlet, which also represents the outlet of the blading, the last blade ring is brought to a higher power output.

The mass flow of the flow flowing through the axial diffuser is smaller in the partial load range than in the base load range, as a result of which the mean flow velocity in the axial diffuser is higher in the base load range than in the partial load range. As a result, the flow in the axial diffuser in the partial load range is more prone to detachment than the flow which occurs at the base load in the axial diffuser.

Thus, the pressure recovery in the axial diffuser at part load is lower compared to the pressure recovery at base load. This has the consequence that at partial load, the turbine power is reduced compared to the turbine power at

Base load. The influence of an improvement in the pressure recovery of a gas turbine diffuser of c _p = 0, l was estimated by Farohki to be 0.8% of the turbine output power. This The same applies to axial-flow steam turbines.

A remedy here could be to reduce the opening degree of the axial diffuser, as this slows down the flow less and thus tends less to detach. However, this lengthens the overall length of the axial diffuser, which adversely increases the overall length of the steam turbine or gas turbine.

The object of the invention is to provide a diffuser arrangement whose pressure recovery is high and whose overall length is small.

Fluid can flow through the diffuser arrangement according to the invention and has an outer diffuser having an inner surface and a flow acceleration device which is set up in such a way that at least part of the boundary layer flow forming on the inner surface of the outer diffuser can be accelerated in the main flow direction, so that a flow separation at the Inner surface of the outer diffuser is prevented.

If the fluid flows through the outer diffuser, it is delayed in the main flow direction, whereby the boundary layer flow which forms on the inner surface of the outer diffuser tends in principle to detach. The detachment would come from a place where the kinetic energy of the flow is zero.

By means of the flow acceleration device according to the invention, at least part of the wall-near flow is accelerated, so that the kinetic energy of the wall-near flow is increased. Thereby, it is prevented that the kinetic energy of the near-wall flow is zero at any location, whereby a flow separation is prevented on the inner surface of the outer diffuser. Thus, the diffuser assembly has a high pressure recovery. Further, the outer diffuser of the diffuser assembly may have a large degree of opening without flow separation occurring therein. As a result, the outer diffuser and thus the diffuser arrangement has a smaller overall length.

The flow acceleration device has a flow guide which extends inside the outer diffuser and with its outer surface facing the inner surface of the outer diffuser and a section of the inner surface of the outer diffuser forms a nozzle channel through which the part of the boundary layer flow can flow.

Thus, the flow accelerating means is constituted by the nozzle passage defined by the flow guide in cooperation with the inner wall of the outer diffuser. It is thereby achieved that immediately adjacent to the inner surface of the outer diffuser the wall-near flow, i. just the flow rate with otherwise low kinetic energy, is accelerated. This effectively prevents separation in the diffuser arrangement.

It is preferred that the flow guiding device, with its inner surface facing away from the outer surface, form an inner diffuser, through which the fluid flow can be flowed and thereby retarded in the main flow direction.

Thus, in addition to the nozzle effect in the outer region, the flow guiding device also has a diffuser effect in the inner region, so that the flow through the diffuser arrangement is greatly delayed. This ensures that the pressure recovery of the diffuser assembly according to the invention is high.

It is further preferred that the extent of the flow guide in the main flow direction is in the range of 5% to 40% of the extent in the main flow direction of the outer end fender. As a result, the flow-guiding device is arranged completely within the outer diffuser and can be placed exactly at that region on the inner wall of the outer diffuser, at which a detachment of the fluid flow is to be expected. Thus, the flow-directing device can be arranged in a targeted manner to a detachment-prone area, whereby an effective prevention of flow separation is achieved and yet the disturbance of the main flow through the flow-guiding device is low.

It is preferred that the outer diffuser and the flow guide are formed axially symmetrical and are arranged concentrically about a common axis of symmetry.

Furthermore, it is preferred that the nozzle channel is formed as an annular channel.

As a result, the diffuser assembly advantageously results as an array of multiple diffusers and a nozzle. This arrangement is formed by a series connection of the three diffusers, namely the area of the outer diffuser upstream of the flow guide, the inner diffuser of the flow guide and the area of the outer diffuser downstream of the flow guide, and a parallel connection of the nozzle channel with the inner diffuser of the flow guide. As a result, a compact, simple and effectively acting subdivision of the outer diffuser is achieved, wherein the diffuser arrangement has a compact design.

Preferably, the flow guide is designed as a straight baffle.

As a result, the guide plate is advantageously producible at low cost.

Alternatively, it is preferred that the flow guide is aerodynamically profiled. As a result, the flow guide has a low flow resistance.

Furthermore, it is preferred that the flow-guiding device is arranged in the range from 80% to 100% of the channel height (radius) of the outer diffuser.

As a result, the flow-guiding device is advantageously effective in the near-wall flow and thereby placed aerodynamically effective.

Furthermore, the flow-guiding device is preferably arranged in the region of the inlet cross-section of the outer diffuser.

As a result, it is advantageously possible for the inlet flow into the outer diffuser of the flow guiding device to already have an accelerated flow in the boundary layer region, which thus does not tend to detach in the course along the inner surface of the outer diffuser.

Furthermore, it is preferred that the flow-guiding device is mounted pivotably relative to the main flow.

This advantageously achieves that the flow guide can be adjusted individually by pivoting relative to the respective flow conditions within the outer diffuser such that the flow guide is aerodynamically effective.

An exhaust steam space of a steam turbine or an exhaust space of a gas turbine preferably has the diffuser arrangement according to the invention.

Furthermore, it is preferred that the flow acceleration device is arranged on the inner surface of the outer diffuser in the region of its inlet. In the following, preferred embodiments of a diffuser arrangement according to the invention will be explained with reference to the attached schematic drawings. It shows:

1 shows a longitudinal section through a first embodiment of the diffuser arrangement,

2 shows a longitudinal section through a second embodiment of the diffuser arrangement,

Fig. 3 is a longitudinal section through a third embodiment of the diffuser assembly and

4 shows a longitudinal section of a diffuser with a schematic representation of the flow conditions.

As can be seen from FIG. 1, a diffuser arrangement 1 has an outer diffuser 2, which is designed to be rotationally symmetrical about its axis of symmetry 3. In a plane perpendicular to the axis of symmetry 3 is an inlet cross-section 4 of the outer diffuser 2, through which an inflow 5 flows into the outer diffuser 2, and in another plane perpendicular to the symmetry axis 3 of the outer diffuser 2 is its outlet cross-section 6, from which an outflow 7 from the

Outside diffuser 2 emerges. Limiting the interior of the outer diffuser 2, this has an inner surface 8.

The outer diffuser 2 is designed as a straight diffuser, i. the inner surface 8 of the outer diffuser 2 forms a truncated cone, the cross-sectional area at the inlet cross-section 4 being smaller than the cross-sectional area at the outlet cross-section 6.

Inside the outer diffuser 2, a flow guide 9 is arranged. The flow guide 9 is formed as an elongated in longitudinal section guide plate, which is rotationally symmetrical about the axis of symmetry of the 3 Exterior diffuser 2 arranged concentric with the

Outer diffuser 2 limits a frusto-conical annular channel, which tapers in the flow direction.

The flow guide 9 has on its outer periphery an outer surface 10 which is inclined relative to the inner surface 8 of the outer diffuser 2 such that the annular space cross-section in a plane perpendicular to the symmetry axis 3, which is formed between the flow guide 9 and the outer diffuser 2, in the flow direction downsized.

That is, the outer surface 10 of the flow guide 9 cooperates with an opposite portion of the inner surface 8 of the outer diffuser 8 such that the annular channel which lies between the flow guide 9 and the outer diffuser 2, a nozzle channel 11 is formed. Thus, the portion of the inner surface 8 of the outer diffuser 2, which faces the outer surface 10 of the flow guiding device 9, is an inner surface 12 of the nozzle channel 11.

Upstream, the flow guide 9 is bounded by its front edge 13 and downstream of its trailing edge 14. In the region of the front edge 13 of the flow guide 9 to the inner surface 8 of the outer diffuser 2 is an inlet cross section 15 of the nozzle channel 11 and in the region of the trailing edge 14 of the flow guide 9 to the inner surface 8 of the outer diffuser 2 is the outlet cross section 16 of the nozzle channel 11, wherein the cross-sectional area of the inlet cross-section 15 is greater than the cross-sectional area of the outlet cross-section 16.

Facing away from the outer surface 10 of the flow-guiding device 9, this has an inner surface 17 which forms an inner diffuser 18. The front edge 13 of the flow guide 9 is arranged in a plane perpendicular to the symmetry axis 3 and forms an inlet cross section 19 of the inner diffuser 18 and the trailing edge 14 of the flow Conducting device 9 is arranged in a plane perpendicular to the symmetry axis 3 and forms an outlet cross section 20 of the inner diffuser 18, wherein the inlet cross section 19 is smaller than the outlet cross section 20.

From Figure 2, the aerodynamic efficiency of the flow guide 9 can be seen. According to Fig. 2, the flow guide 9 is formed as a profiled annular guide plate.

2 shows flow lines 21 in the region of the flow-guiding device 9 and a velocity profile 22 upstream of the flow-guiding device 9, a velocity profile 23 at the trailing edge 14 of the flow-guiding device 9 and a velocity profile 24 downstream of the flow-guiding device 9 shown.

The streamlines 21 have a convergent course in the main flow direction, as a result of which the flow acceleration caused by the flow-guiding device 9 is indicated. The wall normal velocity gradient on the inner surface 8 of the outer diffuser 2 is flatter at the velocity profile upstream of the flow guide 9 than at the velocity profile 23 at the trailing edge 14 of the flow guide 9, which is shallower than the wall normal velocity gradient of the velocity profile 24 downstream of the flow device 9.

As a result, it is shown that the flow which is conducted by the flow-guiding device 9 through the nozzle channel 11 is accelerated (energized). Thus, the flow guide 9 locally increases the velocity of the flow in the vicinity of the inner surface 12 of the outer diffuser 2. In this case, high-energy flow material from the core flow is directed toward the inner surface 12 of the outer diffuser 2 and thus the boundary layer on the inner surface 12 of the outer diffuser 2 supplied. As a result of this energy tion can overcome the boundary layer on the inner surface 12 of the outer diffuser 2 larger positive pressure gradient in the main flow direction without detaching from the inner surface 12 of the outer diffuser 2.

As a result, the outer diffuser 2 reacts more benignly against premature detachment. Thus, by providing the flow guide 9 in the outer diffuser 2, a high pressure recovery of the outer diffuser 2 is achieved.

FIG. 3 shows an exhaust gas space of a gas turbine, which is designed as the outer diffuser 2. The outer diffuser 2 is arranged downstream of a turbine rotor 25 and continues the outflow emerging from the turbine rotor 25 from the inlet cross section 4 of the outer diffuser 2 to the outlet cross section 6 of the outer diffuser 2 under pressure recovery.

The turbine rotor 25 has a turbine rotor hub 26, which is continued by a cylindrical Außenendiffusornabe 27 with the turbine rotor hub 26.

The turbine rotor 25 has a multiplicity of turbine rotor blades 28 which have a blade tip 29 at their radial outer ends. The turbine rotor 25 is surrounded by a turbine housing 30. In operation, the turbine rotor 25 rotates about its axis of rotation (not shown) while the turbine housing 30 remains stationary. Therefore, a gap 31 is provided between the turbine rotor blade tip 29 and the turbine housing 30 so that the turbine rotor blade tip 29 does not touch the turbine housing 30 during operation of the turbine rotor 25.

In order to avoid scratching of the blades on the turbine housing 30 and thus damage, a minimum distance as a gap 31, the so-called game between rotor blade 28 and housing 30 is necessary. Through this gap, a part of the mass flow without power output to the rotor blade 28th flow through and leads to an energization of the boundary layer. Depending on the design of this gap 31 with or without sealing, more or less mass flow can flow through. In order to avoid or greatly delay a subsequent detachment of the flow in the diffuser, further energization of the boundary layer by the flow-guiding device 9 is desired.

According to FIG. 3, by arranging the flow guiding device 9 close to the inner surface 8 of the outer diffuser 2 in the region of the inlet cross section of the outer diffuser 4, a remedy is provided. The boundary layer disturbed by the leakage flow is accelerated by the flow guiding device 9 on the inner surface of the outer diffuser 8 in the main flow direction, so that the kinetic energy in this flow region is increased. This ensures that the flow in the outer diffuser 2 does not detach on the inner surface 8 of the outer diffuser 2. Thus, the flow losses in the outer diffuser 2 are low and the pressure gain of the outer diffuser 2 is high.

Claims

claims

1. A fluid-flowable diffuser arrangement (1) having an inner surface having an outer diffuser (2) and a Strömungsleiteinrichtung (9) having Strömungsbeschleunigungseinrichtung, the Strömungsleiteinrichtung (9) extends within the outer diffuser (2) and with its the inner surface ( 8) of the outer diffuser (2) facing outer surface (10) and a portion of the inner surface (8) of the outer diffuser (2) forms a nozzle channel (11), whereby at least a part of the inner surface (8) of the outer diffuser (2) are formed Boundary layer flow in the main flow direction can be accelerated, so that a flow separation on the inner surface (8) of the outer diffuser (2) is prevented.

2. Diffuser assembly (1) according to claim 1, wherein the flow guide (9) has a fluid vorströmmbare front edge (13) and one of these opposite trailing edge (14), at which the fluid can be flowed off, and wherein between the inner surface (8). the outer diffuser (2) and the front edge (13) of the flow-guiding device (9) has an inlet cross-section (15) and an outlet cross-section (8) between the inner surface (8) of the outer diffuser (2) and the trailing edge (14) of the flow-guiding device (9) 16), wherein the cross-sectional area of the inlet cross-section (13) is greater than the cross-sectional area of the outlet cross-section (16).

3. diffuser assembly (1) according to claim 1 or 2, wherein the flow-guiding device (9) with their their

Outside surface (10) facing away from inner surface (17) forms an inner diffuser (18), through which the fluid flow flowable and can be delayed in the main flow direction.

4. diffuser assembly (1) according to claim 1, 2 or 3, wherein in the main flow direction, the extension of the flow guide (9) in the range of 5% to 40% of the extent of the outer diffuser (2).

5. diffuser assembly (1) according to one of claims 1 to 4, wherein the outer diffuser (2) and the flow guide (9) are formed axially symmetrical and about a common axis of symmetry (3) are arranged concentrically.

6. Diffuser arrangement (1) according to one of claims 1 to 5, wherein the nozzle channel (11) is designed as an annular channel.

7. diffuser assembly (1) according to one of claims 1 to 6, wherein the flow guide (9) is formed as a straight, elongated in longitudinal section baffle or aerodynamically profiled.

8. diffuser assembly (1) according to one of claims 1 to 7, wherein the flow guide (9) in the range of 80% to 100% of the channel height of the outer diffuser (2) is arranged.

9. diffuser arrangement (1) according to one of claims 1 to 8, wherein the flow-guiding device (9) in the region of the inlet cross-section (4) of the outer diffuser (2) is arranged.

10. diffuser assembly (1) according to one of claims 1 to 9, wherein the outer diffuser (2) is designed as a substantially straight diffuser.

11. diffuser assembly (1) according to one of claims 1 to 10, wherein the flow guide (9) is mounted pivotably relative to the main flow direction.

12. Abdampfräum a steam turbine, with a diffuser assembly (1) according to any one of claims 1 to 11.

13. exhaust gas space of a gas turbine, with a diffuser arrangement (1) according to one of claims 1 to 11.